The present invention relates to child swings, and particularly to a child swing having a swing mounted on a support stand for pendulum motion. More particularly, the present invention relates to a child swing having a swing driver that is energized by electricity to sustain swinging movement of the swing.
Any rigid body mounted so that it can swing in a vertical plane about some axis passing through it under the influence of gravity is called a physical pendulum. A swing seat mounted on a frame for swinging movement about a swing axis is an example of a physical pendulum because the swing seat can swing backward and forward along a swing arc like a pendulum in a grandfather's clock.
Pendulums such as swing seats swing along a swing arc back and forth between first and second extreme positions. "Amplitude" is understood to be the extent of angular movement of a pendulum measured from the first extreme position to the second extreme position.
The motion of a pendulum is periodic and oscillatory. Any motion that repeats itself in equal intervals of time is called periodic motion. A body in periodic motion that moves back and forth over the same path undergoes oscillatory motion. The "period" of motion of a pendulum is understood to be the interval of time required for the pendulum to complete a cycle and begin to repeat itself. A cycle is one complete round trip of motion (e.g., swinging movement of a pendulum from the first extreme position to the second extreme position and back to the first extreme position).
The period of any pendulum is a function of (1) gravity; (2) the distance between the center of gravity of the pendulum and the axis about which the pendulum swings, and (3) the amplitude of the pendulum (especially in circumstances where the pendulum amplitude is greater than a few degrees). The period of a pendulum is typically measured in seconds per cycle. It is important to understand that the period of a pendulum is independent of the mass of the pendulum.
The natural frequency of a pendulum is the number of cycles completed by the pendulum per unit time when the pendulum is displaced and then released. The natural frequency of a pendulum is also a function of the three factors noted above in the discussion about the period of a pendulum. The natural frequency of a pendulum is independent of the mass of the pendulum and is typically measured in cycles per second.
A pendulum would oscillate indefinitely if no frictional or wind-resistance forces acted on the pendulum. Actually, the amplitude of oscillation of a pendulum gradually decreases to zero as a result of friction and wind-resistance forces acting on the pendulum as it swings unless some oscillatory external force is applied to the pendulum. In some cases, in an attempt to sustain swinging movement of a pendulum, the pendulum is subjected to an oscillatory external force having a frequency that is different than the natural frequency of the pendulum. The response of the pendulum depends on the relation between the "forced" and natural frequency.
In accordance with the present invention, a swing assembly includes a support stand, a swing mounted on the support stand to swing back and forth along a swing arc, and a swing driver. The swing driver includes a drive belt coupled to the swing, a belt tensioner coupled to the drive belt to place the drive belt in tension, and a belt driver coupled to the drive belt. The belt driver moves the drive belt relative to the support stand while the drive belt remains in tension to apply force to the swing to sustain swinging movement of the swing along the swing arc. The drive belt includes a strap having a fixed end coupled to the support stand and a free end coupled to the belt tensioner. The drive belt has drive teeth that are appended to the strap and coupled to the belt driver.
In preferred embodiments, the swing includes a drive shaft mounted for rotation on the support stand. A swing seat frame and a drive member are both coupled to the drive shaft for conjoint rotation. The drive belt is coupled to the drive member. The drive member has a drive lever with a base end coupled to the drive shaft and a free end spaced apart from the base end. A lever wheel is mounted on the free end for rotation about an axis of rotation and the drive belt wraps around a portion of the lever wheel. The strap has a first side carrying the drive teeth and a second side providing a friction surface engaging the lever wheel.
The belt driver includes an electric motor, a motor shaft turned by the electric motor, and a drive gear carried on the motor shaft for rotation therewith. The drive teeth on the strap engage the drive gear.
The belt tensioner includes a belt support including a support base, a spring wheel rotatable about an axis of rotation relative to the support base, and a constant-force spring acting between the support base and the spring wheel. The belt tensioner is positioned to lie between the drive shaft and the lever wheel during rotation of the drive member about the axis of rotation.
The free end of the drive belt is coupled to the spring wheel to rotate with it about the axis of rotation. The spring wheel includes an outer wall engaging the drive belt and an inner wall defining a spring cavity. The constant-force spring is positioned to lie in the spring cavity. The constant-force spring includes a fixed end coupled to the support base and a free end coupled to the inner wall of the spring wheel.
Additional features of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the presently perceived best mode of carrying out the invention.